System and method for coded communication signals regulating inductive power transmission

ABSTRACT

An inductive power transfer system and method for transferring power to an electrical device wirelessly includes an inductive power outlet and an inductive power receiver. During operation, instruction signals are sent from the inductive power outlet to the inductive power receiver. When no instruction signals are transferred, the system is configured to deactivate such that power is drawn by the system only during operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 13/205,672filed Aug. 9, 2011, which is a continuation-in-part of U.S. applicationSer. No. 12/497,088 filed Jul. 2, 2009, now U.S. Pat. No. 8,188,619,issued May 29, 2012, which, in turn, claims the benefit of U.S.provisional applications No. 61/129,526 filed Jul. 2, 2008 and No.61/129,859 filed Jul. 24, 2008, the disclosures of all of which arehereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention is directed to providing energy efficientinductive power transfer. More specifically, the present inventionrelates to inductive power transfer systems and methods incorporatingactivation and termination mechanisms.

BACKGROUND OF THE INVENTION

The efficient use of available energy is of great importance for anumber of reasons. On a global scale, there is increasing concern thatthe emission of greenhouse gases such as carbon dioxide from the burningof fossil fuels may precipitate global warming. Moreover, energyresources are limited. The scarcity of global energy resources alongsidegeopolitical factors drives the cost of energy upwards. Thus efficientuse of energy is an ever more important budget consideration for theenergy consumer.

Energy losses in electrical energy transmission are chiefly due to theincidental heating of current carrying wires. In many cases this isunavoidable, as current carrying wires are essential for the powering ofelectrical devices and current carrying wires have resistance. It is thework done to overcome this resistance which generates heat in the wires.

In other cases the energy losses are unnecessary. For example,electrical devices are often left running unnecessarily and energy usedto power devices which are not being used is truly wasted. Variousinitiatives aimed at reducing the amount of energy wasted by idledevices have been proposed. For example, Energy Star is a joint programof the United States Environmental Protection Agency and the UnitedStates Department of Energy which awards manufacturers the right todisplay a recognizable label on products which meet certain energyconsumption standards. Energy Star attempts to reduce energy consumptionthrough better energy management.

Efficient energy management reduces energy wastage. For example, laptopcomputers, which rely upon a limited amount of energy supplied fromonboard power cells, use a variety of strategies for keeping powerconsumption to a minimum. Thus the screen and hard drives are switchedoff automatically after the computer has been left inactive for asignificant length of time, similarly the network card may be disabledwhen the computer is disconnected from the mains or from a network. Suchenergy management strategies may serve to increase the length of timethat a device can be powered by its onboard cells.

Even when connected to the mains, however, efficient use of energy isessential. Many common electrical devices run on low voltage DC andtypically use a transformer with an AC-DC power adapter to control thepower provided to it. Energy Star estimates that 1.5 billion such poweradapters are used in the United States alone for devices such as MP3players, Personal Digital Assistants (PDAs), camcorders, digitalcameras, emergency lights, cordless and mobile phones. According toEnergy Star, such power adapters draw about 300 billion kilowatt-hoursof energy every year which is approximately 11% of the United States'national electric bill.

If multiple devices could be run from a single power adapter this wouldgreatly reduce the number of power adapters in use. However, the supplyof electricity to a number of devices through a single cable is nottrivial. The more devices that are connected to a single power strip thegreater the current which is drawn by the strip. Thus the currentsupplied through the single cable connecting the power strip to themains increases.

Power losses due to the heating of a cable increase according to thesquare of the current it carries so energy losses from the cable mayincrease parabolically. Furthermore, in the absence of effective energymanagement, if too many devices draw current from a single cable thecurrent supplied may exceed the permitted level thereby tripping acircuit breaker or blowing a fuse. Even more seriously, the excessivecurrent may lead to overheating of the cable which is a common cause offire.

A further unnecessary usage of energy is in powering of devices havingonboard power cells. When an electric device having rechargeable cellssuch as a laptop computer, electric shaver or the like, is connected tothe mains power is drawn both to operate the device and also to rechargethe cells. Although electrical cells do need to be rechargedperiodically, even partially charged cells are sufficient to power thedevice. It is unnecessary therefore to continuously charge the onboardcell.

Furthermore, the energy needlessly consumed charging electrical cellsbeyond the level necessary for operation of a device increaseselectricity bills. This is of particular concern where a large number ofsuch devices are being used simultaneously. For example for a companywhich hosts a meeting or a conference where many individual laptopcomputers are being used simultaneously.

Inductive power coupling allows energy to be transferred from a powersupply to an electric load without a wired connection therebetween. Anoscillating electric potential is applied across a primary inductor.This sets up an oscillating magnetic field in the vicinity of theprimary inductor. The oscillating magnetic field may induce a secondaryoscillating electrical potential in a secondary inductor placed close tothe primary inductor. In this way, electrical energy may be transmittedfrom the primary inductor to the secondary inductor by electromagneticinduction without a conductive connection between the inductors.

When electrical energy is transferred from a primary inductor to asecondary inductor, the inductors are the to be inductively coupled. Anelectric load wired in series with such a secondary inductor may drawenergy from the power source wired to the primary inductor when thesecondary inductor is inductively coupled thereto.

The strength of the induced voltage in the secondary inductor variesaccording to the oscillating frequency of the electrical potentialprovided to the primary inductor. The induced voltage is strongest whenthe oscillating frequency equals the resonant frequency of the system.The resonant frequency f_(R) depends upon the inductance L and thecapacitance C of the system according to the equation

$f_{R} = {\frac{1}{2\; \pi \sqrt{LC}}.}$

Known inductive power transfer systems typically transmit power at theresonant frequency of the inductive couple. This can be difficult tomaintain as the resonant frequency of the system may fluctuate duringpower transmission, for example in response to changing environmentalconditions or variations in alignment between primary and secondarycoils.

Amongst others, one problem associated with resonant transmission is thehigh transmission voltages involved. At high operating voltages, a largeamount of heat may be generated by the system resulting in high powerlosses as well as damage to heat sensitive components. Accordingly,capacitors and transistors in the resonant circuits may need to berelatively large.

The need remains therefore for an energy efficient inductive powertransfer system which may incur lower power losses during operation. Thecurrent disclosure addresses this need.

SUMMARY

According to one aspect of the disclosure an inductive power outlet ispresented for transmitting power to at least one inductive powerreceiver. The inductive power outlet comprises at least one primaryinductor wired to a power supply, the primary inductor for forming aninductive couple with at least one secondary inductive coil associatedwith the inductive power receiver; and at least one driver configured toprovide an oscillating voltage across the primary inductor.

The inductive power receiver may comprise the at least one secondaryinductive coil; and an output regulator operable to monitor inducedvoltage across the secondary inductive coil; to detect an activationvoltage pulse; to compare the induced voltage with at least onethreshold value; to send at least one instruction signal to theinductive power outlet; and to provide power to an electric load.

The inductive power outlet may be operable to induce an activationvoltage pulse across the secondary inductive coil of the inductive powerreceiver thereby initiating the inductive power receiver to send anidentification signal to the inductive power outlet and to start drawingpower therefrom.

Optionally, the inductive power receiver further comprises a signaltransmission circuit operable to generate the at least one instructionsignal. The transmission circuit may comprise at least one ancillaryload selectively connectable to the secondary inductor by a switchingunit, wherein the switching unit is configured to connect the ancillaryload to the secondary inductor with a characteristic frequency therebyproducing a pulse of detectable peaks in primary voltage or primarycurrent having the characteristic frequency.

Optionally, the at least one instruction signal comprising a pulse mayhave a characteristic frequency of peaks in primary voltage or primarycurrent, wherein the inductive power outlet further comprises: at leastone peak detector configured to detect the peaks; and at least oneprocessor operable to determine the characteristic frequency of thepeaks.

-   -   In other embodiments, the outlet further comprises a signal        detector operable to detect the instruction signals and the        driver is operable to perform at least one function selected        from a group consisting of:    -   selecting a first operating power if the signal detector detects        a first instruction signal;    -   selecting a second operating power if the signal detector        detects a second instruction signal;    -   increasing operating power by a first increment if the signal        detector detects a third instruction signal;    -   increasing operating power by a second increment if the signal        detector detects a fourth instruction signal;    -   decreasing operating power by a first increment if the signal        detector detects a fifth instruction signal;    -   decreasing operating power by a second increment if the signal        detector detects a sixth instruction signal;    -   continuing to provide the oscillating voltage across the primary        inductor at same power if the signal detector detects a seventh        instruction signal; and    -   ceasing to provide the oscillating voltage across the primary        inductor if the signal detector detects an eighth instruction        signal.

The inductive power outlet may further comprise a trigger sensorconfigured to detect a release signal indicating proximity of a possibleinductive power receiver.

Optionally, the activation voltage pulse comprises an induced voltageacross the secondary inductive coil of at least eight volts. Whereappropriate, the activation voltage pulse produces a current of at leastthree milliamps.

According to a further aspect of the disclosure an inductive powerreceiver is presented for receiving power from at least one inductivepower outlet. The inductive power receiver may comprise at least onesecondary inductor for forming an inductive couple with at least oneprimary inductive coil; and at least one signal transmission circuitconfigured to generate at least one instruction signal, the instructionsignal being detectable by a signal detector associated with theinductive power outlet as a pulse having a characteristic frequency ofpeaks in primary voltage or primary current. Where required, theinductive power outlet may be configured to drive an oscillating voltageacross the primary inductive coil for a limited time duration and tostop driving the oscillating voltage if no instruction signal isreceived during the time duration; and the transmission circuit may beoperable to send at least one instruction signal to the inductive poweroutlet during each the time duration.

Optionally, the time duration is between five milliseconds and tenmilliseconds.

In some embodiments, at least one instruction signal comprises atermination signal and the inductive power outlet is operable to ceasedriving the primary inductive coil when the termination signal isdetected.

Where appropriate, the transmission circuit may comprise a signalgenerator operable to generate at least one instruction signal having acharacteristic frequency selected from at least one of a groupconsisting of: 250 hertz, 500 hertz, 1 kilohertz, from 1.5 kilohertz to5 kilohertz and 8 kilohertz.

Optionally, the inductive power receiver further comprises an outputregulator operable to monitor induced voltage across the secondaryinductor; to compare the induced voltage with at least one thresholdvalue; and to provide power to an electric load. The output regulatormay be further operable to generate at least one instruction signalselected from a group consisting of:

-   -   an initial pulse of approximately one kilohertz to instruct the        inductive power outlet to drive the primary inductive coil at a        first operating power;    -   an initial pulse of approximately 8 kilohertz to instruct the        inductive power outlet to drive the primary inductive coil at a        second operating power;    -   a pulse of approximately one kilohertz to instruct the inductive        power outlet to increase operating power by a first increment;    -   a pulse of between approximately 1.5 kilohertz and approximately        5 kilohertz to instruct the inductive power outlet to increase        operating power by a second increment;    -   a pulse of approximately 8 kilohertz to instruct the inductive        power outlet to decrease operating power by a first increment;    -   a pulse of approximately 500 hertz to instruct the inductive        power outlet to continue driving the primary inductive coil at        the same power; and    -   a pulse of approximately 250 hertz to instruct the inductive        power outlet to cease driving the primary inductive coil.

In another aspect of the disclosure, a method is taught for transferringpower inductively comprising: obtaining an inductive power outletcomprising: at least one primary inductor, at least one driver and atleast one instruction signal detector; obtaining an inductive powerreceiver comprising: at least one secondary inductor and at least oneinstruction signal generator; driving the primary inductor for a limitedtime duration; monitoring the signal detector; if at least oneinstruction signal is detected by the instruction signal detector duringthe time duration, then repeating steps of driving the primary inductorand monitoring the signal detector; and if no instruction signal isreceived during the time duration, then terminating the driver.Optionally, the time duration is between five milliseconds and tenmilliseconds.

Variously, the method may further comprise at least one of:

-   -   if the instruction signal detector detects a termination signal,        then terminating the driver;    -   if the instruction signal detector detects a perpetuation        signal, then continuing to drive the primary inductor with the        same power;    -   if the instruction signal detector detects a first increase        power signal, then increasing power by a first incremental        value;    -   if the instruction signal detector detects a second increase        power signal, then increasing power by a second incremental        value; and    -   if the instruction signal detector detects a decrease power        signal, then decreasing power by an incremental value.

Where appropriate, the instruction signal generator comprises a signaltransmission circuit operable to draw additional power from thesecondary inductive coil thereby generating detectable peaks in primaryvoltage or primary current. Optionally, the instruction signal detectorcomprises at least one peak detector configured to detect peaks inprimary voltage or primary current; and at least one processor operableto determine the characteristic frequency of the peaks;

Additionally or alternatively, the method may further comprise at leastone of:

-   -   if the peak detector initially detects peaks in primary voltage        or primary current having a first characteristic frequency then        the driver operating at a first operating power;    -   if the peak detector initially detects peaks in primary voltage        or primary current having a second characteristic frequency then        the driver operating at a second operating power;    -   if the peak detector detects peaks in primary voltage or primary        current having a third characteristic frequency then the driver        increasing operating power by a first increment;    -   if the peak detector detects peaks in primary voltage or primary        current having a fourth characteristic frequency then the driver        increasing operating power by a second increment;    -   if the peak detector detects peaks in primary voltage or primary        current having a fifth characteristic frequency then the driver        decreasing operating power by a first increment;    -   if the peak detector detects peaks in primary voltage or primary        current having a sixth characteristic frequency then the driver        decreasing operating power by a second increment;    -   if the peak detector detects peaks in primary voltage or primary        current having a seventh characteristic frequency then the        driver continuing to operate at same power; and    -   if the peak detector detects peaks in primary voltage or primary        current having an eighth characteristic frequency then the        driver ceasing to provide the oscillating voltage.

Variously, the characteristic frequency may be selected from at leastone of a group consisting of: 250 hertz, 500 hertz, 1 kilohertz, from1.5 kilohertz to 5 kilohertz, 8 kilohertz or the like.

Other embodiments of the present invention are directed towardsproviding an inductive power transfer system comprising at least oneinductive power outlet comprising at least one primary inductive coilwired to a power supply via a driver; the primary inductive coil forforming an inductive couple with at least one secondary inductive coilwired to an electric load, the secondary inductive coil associated withan inductive power receiver wherein the driver is configured to providea driving voltage across the primary inductive coil, the driving voltageoscillating at a transmission frequency significantly different from theresonant frequency of the inductive couple. Optionally, the drivercomprises a switching unit for intermittently connecting the primaryinductive coil to the power supply.

Optionally, the transmission frequency lies within a range in whichinduced voltage varies approximately linearly with frequency.Optionally, the driver is configured to adjust the transmissionfrequency in response to the feedback signals.

Optionally, the inductive power outlet comprising a signal detectoradapted to detect a first signal and a second signal, and the driver isconfigured to: increase the transmission frequency when the first signalis detected by the detector, and decrease the transmission frequencywhen the second signal is detected by the detector. The feedback signalsgenerally carry data pertaining to the operational parameters of theelectric load. Operational parameters are selected from the groupcomprising: required operating voltage for the electric load; requiredoperating current for the electric load; required operating temperaturefor the electric load; required operating power for the electric load;measured operating voltage for the electric load; measured operatingcurrent for the electric load; measured operating temperature for theelectric load; measured operating power for the electric load; powerdelivered to the primary inductive coil; power received by the secondaryinductive coil, and a user identification code. Optionally, the detectoris selected from the list comprising optical detectors, radio receivers,audio detectors and voltage peak detectors.

Optionally, the driver further comprises a voltage monitor formonitoring the amplitude of a primary voltage across the primary coil.Optionally, the voltage monitor is configured to detect significantincreases in primary voltage.

In other embodiments, the driving voltage oscillating at a transmissionfrequency higher than the resonant frequency of the inductive couple,wherein the primary inductive coil is further wired to a receptioncircuit comprising a voltage monitor for monitoring the amplitude of aprimary voltage across the primary coil, and the secondary inductivecoil is further wired to a transmission circuit for connecting at leastone electric element to the secondary inductive coil thereby increasingthe resonant frequency such that a control signal may be transferredfrom the transmission circuit to the reception circuit. Optionally, thesecondary inductive coil is wired to two inputs of a bridge rectifierand the electric load is wired to two outputs of the bridge rectifierwherein the transmission circuit is wired to one input of the bridgerectifier and one output of the bridge rectifier. Typically, thetransmission circuit further comprises a modulator for modulating abit-rate signal with an input signal to create a modulated signal and aswitch for intermittently connecting the electrical element to thesecondary inductive coil according to the modulated signal. Optionally,the voltage monitor further comprises a correlator for cross-correlatingthe amplitude of the primary voltage with the bit-rate signal forproducing an output signal.

In certain embodiments, the control signal is for transferring afeedback signal from the secondary inductive coil to the primaryinductive coil for regulating power transfer across an inductive powercoupling. The driver may be configured to adjust the transmissionfrequency in response to the feedback signals. Typically, the system isadapted to transfer a first signal and a second signal, and the driveris configured to: increase the transmission frequency when the firstsignal is received by the receiver, and decrease the transmissionfrequency when the second signal is received by the receiver.

Variously, embodiments of the invention may be incorporated into atleast one application selected from a group consisting of: inductivechargers, inductive power adaptors, power tools, kitchen appliances,bathroom appliances, computers, media players, office equipment,implanted devices, pace makers, trackers and RFID tags inductivechargers, inductive power adaptors

It is a further aim of the current invention to teach a method forregulating power transmission inductive from a primary inductive coil,wired to a power supply via a driver, to a secondary inductive coil,wired to an electric load, the method comprising the following steps:(a)—providing an oscillating voltage to the primary inductive coil at aninitial transmission frequency ft which is substantially different fromthe resonant frequency f_(R) of the system; (b)—inducing a secondaryvoltage in the secondary inductive coil; (c)—monitoring power receivedby the electric load; (d)—sending a feedback signal when the monitoredpower deviates from a predetermined range; (e)—the driver receiving thefeedback signal; (f)—the driver adjusting the transmission frequency;and (g)—repeating steps (b)-(f).

Optionally, step (d) further comprises: (d1) sending a feedback signalof a first type S_(a) to the driver, whenever the power drops below apredetermined lower threshold, and (d2) sending a feedback signal of asecond type S_(b) to the driver, whenever the power exceeds apredetermined upper threshold.

According to preferred embodiments the initial transmission frequencyf_(t) is higher than the resonant frequency f_(R) and step (f) furthercomprises: (f1) the driver reducing the transmission frequency by anincremental value −δf₁ when the received feedback signal is of the firsttype S_(a), and (f2) the driver increasing the transmission frequency byan incremental value +δf₂ when the received feedback signal is of thesecond type S_(b).

In still other embodiments, the invention is directed to teachinganother method for transferring a signal from a secondary inductive coilto a primary inductive coil of an inductive power transfer system, themethod comprising the following steps: Step (i)—connecting the primaryinductive coil to a voltage monitor for monitoring the amplitude of aprimary voltage across the primary coil; Step (ii)—connecting thesecondary inductive coil to a transmission circuit for selectivelyincreasing the resonant frequency of the inductive power transfersystem; Step (iii)—providing an oscillating voltage to the primaryinductive coil at an initial transmission frequency higher than theresonant frequency thereby inducing a voltage in the secondary inductivecoil; Step (iv)—using the transmission circuit to modulate a bit-ratesignal with the input signal to create a modulated signal and connectingthe electrical element to the secondary inductive coil intermittentlyaccording to the modulated signal, and Step (v)—using the voltagemonitor to cross-correlate the amplitude of the primary voltage with thebit-rate signal for producing an output signal.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the invention and to show how it may becarried into effect, reference will now be made, purely by way ofexample, to the accompanying drawings.

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention; the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice. In the accompanying drawings:

FIG. 1 is a block diagram showing the main elements of an inductivepower transfer system with a feedback signal path according toembodiments of the present invention;

FIG. 2 is a graph showing how the amplitude of operational voltage of aninductive power transfer system varies with transmission frequency;

FIG. 3 is a schematic diagram representing a laptop computer drawingpower from an inductive power outlet;

FIG. 4 is a circuit diagram of an inductive power transfer systemaccording to another embodiment of the invention including a peakdetector for detecting large increases in transmission voltage;

FIG. 5 is a flowchart showing a method for regulating power transfer byvarying the power transmission frequency in an inductive power transfersystem according to a further embodiment of the invention;

FIG. 6 is a block diagram showing the main elements of an inductivepower transfer system with an inductive feedback channel according tostill another embodiment of the present invention;

FIG. 7 is a graph showing how the variation of operational voltage withtransmission frequency is effected by changes in resonant frequency ofthe system;

FIG. 8 is a circuit diagram of an inductive power transfer systemincluding an inductive feedback channel for providing coil-to-coilsignal transfer concurrently with uninterrupted inductive power transferbetween the coils in accordance with yet another embodiment of theinvention;

FIG. 9 is a flowchart showing a method for inductively transferring asignal from the secondary inductive coil to a primary inductive coil ofan inductive power transfer system according to still a furtherembodiment of the invention;

FIG. 10A is a block diagram representing selected components of anenergy efficient inductive power transfer system incorporatingactivation and termination mechanisms;

FIG. 10B is a flowchart representing transition between standby mode andtransmission mode for activating and terminating an energy efficientinductive power transfer system;

FIG. 11A is a flowchart representing selected stages of a possibleprotocol for transition from standby phase to the transmission phase inthe inductive power outlet of an energy efficient inductive poweroutlet;

FIG. 11B is a flowchart representing a possible transmission modeprotocol for an inductive power outlet; and

FIG. 11C is a flowchart representing operation of an energy efficientinductive power receiver.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made to FIG. 1 showing a block diagram of the mainelements of an inductive power transfer system 100 adapted to transmitpower at a non-resonant frequency according to another embodiment of theinvention. The inductive power transfer system 100 consists of aninductive power outlet 200 configured to provide power to a remotesecondary unit 300. The inductive power outlet 200 includes a primaryinductive coil 220 wired to a power source 240 via a driver 230. Thedriver 230 is configured to provide an oscillating driving voltage tothe primary inductive coil 220.

The secondary unit 300 includes a secondary inductive coil 320, wired toan electric load 340, which is inductively coupled to the primaryinductive coil 220. The electric load 340 draws power from the powersource 240. A communication channel 120 may be provided between atransmitter 122 associated with the secondary unit 300 and a receiver124 associated with the inductive power outlet 200. The communicationchannel 120 may provide feedback signals S and the like to the driver230.

In some embodiments, a voltage peak detector 140 is provided to detectlarge increases in the transmission voltage. As will be descried belowthe peak detector 140 may be used to detect irregularities such as theremoval of the secondary unit 200, the introduction of power drains,short circuits or the like.

FIG. 2 is a graph showing how the amplitude of the operational voltageof an inductive power transfer system varies according to thetransmission frequency. It is noted that the voltage is at its highestwhen the transmission frequency is equal to the resonant frequency f_(R)of the system, this maximum amplitude is known as the resonance peak 2.It is further noted that the slope of the graph is steepest in theregions 4 a, 4 b to either side of the resonance peak 2. Thus ininductive transfer systems, which operate at or around resonance, asmall variation in frequency results in a large change in inducedvoltage. Similarly, a small change in the resonant frequency of thesystem results in a large change in the induced voltage. For this reasonprior art resonant inductive transfer systems are typically verysensitive to small fluctuations in environmental conditions orvariations in alignment between the induction coils.

It is a particular feature of embodiments of the current invention thatthe driver 230 (FIG. 1) is configured and operable to transmit a drivingvoltage which oscillates at a transmission frequency which issubstantially different from the resonant frequency of the inductivecouple. Optionally the transmission frequency is selected to lie withinone of the near-linear regions 6, 8 where the slope of thefrequency-amplitude graph is less steep.

One advantage of this embodiment of the present invention may bedemonstrated with reference now to FIG. 3. A schematic diagram is shownrepresenting a laptop computer 340 drawing power from an inductive poweroutlet 200 via a secondary power receiving unit 300. The power receivingunit 300 includes a secondary inductive coil 320 which is aligned to aprimary inductive coil 220 in the inductive power outlet 200. Anylateral displacement of the secondary power receiving unit 300 changesthe alignment between the secondary inductive coil 320 to the primaryinductive coil 220. As a result of the changing alignment, the combinedinductance of the coil pair changes which in turn changes the resonantfrequency of the system.

If the inductive power outlet 200 transmits power at the resonantfrequency of the system, even a small lateral movement would reducesignificantly the amplitude of the induced voltage. In contradistinctionto the prior art, in embodiments of the present invention the inductivepower outlet 200 transmits power at a frequency in one of the regions 6,8 to either side of the resonance peak 2 (FIG. 2) where the slope of theresonance graph is much shallower. Consequently, the system has a muchlarger tolerance of variations such as lateral movement.

A further feature of embodiments of inductive power outlets transmittingat frequencies above the natural resonant frequency of the system, isthat if the resonant frequency of the system increases for some reasons,then the transmission voltage increases sharply. In preferredembodiments, a peak detector 140 (FIG. 1) is be provided to monitor thetransmission voltage of the power outlet 200 and is configured to detectlarge increases in the transmission voltage indicating an increase inresonant frequency.

Referring again to the resonant formula for inductive systems,

${f_{R} = \frac{1}{2\; \pi \sqrt{LC}}},$

it is noted that any decrease in either the inductance L or thecapacitance C of the system increases the resonant frequency and may bedetected by the peak detector 140.

As an example of the use of a peak detector 140, reference is again madeto FIG. 3. It will be appreciated that in a desktop environment,conductive bodies such as a paper clip, metal rule, the metal casing astapler, a hole-punch or any metallic objects may be introduced betweenthe inductive power outlet 200 and the secondary power receiving unit300. The oscillating magnetic field produced by the primary coil 220would then produce eddy currents in the conductive body heating it andthereby draining power from the primary coil 220. Such a power drain maybe wasteful and/or dangerous. Power drains such as described abovegenerally reduce the inductance L of the system thereby increasing itsresonant frequency.

The inductance L of the system may also be reduced by the removal of thesecondary coil 220, the creation of a short circuit or the like. A peakdetector 140, wired to the inductive power outlet, may detect any ofthese scenarios as a large increase in transmission voltage. Whererequired, the power transfer system may be further configured to shutdown, issue a warning or otherwise protect the user and the system inthe event that the peak detector 140 detects such an increase intransmission voltage.

FIG. 4 is a circuit diagram of an inductive power outlet 6200 andsecondary unit 6300. The secondary unit 6300 comprises a secondary coil6320 wired to an electric load 6340 via a rectifier 6330.

The inductive power outlet 6200 comprises a primary coil 6220 driven bya half-bridge converter 6230 connected to a power source 6240. Thehalf-bridge converter 6230 is configured to drive the primary coil 6220at a frequency higher than the resonant frequency of the system and apeak detector 6140 is configured to detect increases in the transmissionvoltage.

Although only a half-bridge converter is represented in FIG. 4, it isnoted that other possible driving circuits include: a DC-to-DCconverter, an AC-to-DC converter, an AC-to-AC converter, a flybacktransformer, a full-bridge converter, a flyback converter or a forwardconverter for example.

Another advantage of non-resonant transmission is that the transmissionfrequency may be used to regulate power transfer. Prior art inductivepower transfer systems, typically regulate power transfer by alteringthe duty cycle of the transmission voltage. Unlike prior art systems,because embodiments of the present invention transmit at a frequency notequal to the resonant frequency of the system, the driver 230 may beconfigured to regulate power transfer by adjusting the transmissionfrequency.

The regulation is illustrated with reference to FIG. 2. In embodimentsof the invention, the frequency of transmission may be selected to be inthe approximately linear region 8 of the curve between a lower frequencyvalue of f_(L) and an upper frequency value of f_(U). A transmissionfrequency f_(t), higher than the resonant frequency f_(R) of the system,produces an induced voltage of V_(t). The induced voltage can beincreased by reducing the transmission frequency so that it is closer tothe resonant frequency f_(R). Conversely, the induced voltage may bereduced by increasing the transmission frequency so that it is furtherfrom the resonant frequency f_(R). For example, an adjustment oftransmission frequency by δf produces a change in induced voltage of δV.

In some embodiments, a communication channel 120 (FIG. 1) is providedbetween the secondary unit 300 and the inductive power outlet 200 tocommunicate the required operating parameters. In embodiments of theinvention operating parameters the communication channel 120 may be usedto indicate the transmission frequency required by the electric load 340to the driver 230.

The communication channel 120 may further provide a feedback signalduring power transmission. The feedback transmission may communicaterequired or monitored operating parameters of the electric load 240 suchas:

-   -   required operating voltage, current, temperature or power for        the electric load 240,    -   the measured voltage, current, temperature or power supplied to        the electric load 240 during operation,    -   the measured voltage, current, temperature or power received by        the electric load 240 during operation and the like.

In some embodiments, a microcontroller in the driver 230 may use suchfeedback parameters to calculate the required transmission frequency andto adjust the driver accordingly. Alternatively, simple feedback signalsmay be provided indicating whether more or less power is required.

One example of a power regulation method using simple feedback signalsis shown in the flowchart of FIG. 5. The method involves the followingsteps:

-   Step (a)—The driver 230 provides an oscillating voltage at a    transmission frequency f_(t) which is higher than the resonant    frequency f_(R) of the system.-   Step (b)—A secondary voltage is induced in the secondary coil 320.-   Step (c)—A power monitor in the secondary unit 300, monitors the    power received by the electric load 340.-   Step (d)—If the power received by the electric load 340 lies within    a predetermined range then no action is taken. If the power received    by the electric load 340 is below the predetermined range, then a    feedback signal of a first type S_(a) is sent to the driver. If the    power received by the electric load 340 is above the predetermined    range, then a feedback signal of a second type S_(b) is sent to the    driver.-   Step (e)—A feedback signal is received by the driver 230.-   Step (f)—If the received feedback signal is of the first type S_(a),    then the transmission frequency is increased by an incremental value    +δf₁. If the received feedback signal is of the second type S_(b),    then the transmission frequency is decreased by an incremental value    −δf₂.

It is noted that by using the power regulation method described above,when the power received by the load is too high, a series of feedbacksignals of the first type S_(a) will be transmitted until the power isreduced into the acceptable range. Likewise when the power received bythe load is too low, a series of feedback signals of the second typeS_(b) will be transmitted until the power is increased into theacceptable range. It is noted that the positive incremental value δf₁may be greater than, less than or equal to the negative incrementalvalue δf₂.

Alternatively, other power regulation methods using frequency adjustmentmay be used. For example, the operating parameters of the electric loadmay be monitored and their values may be transmitted to the power outletvia the communications channel 120. A processor in the power outlet maythen calculate the required transmission frequency directly.

The method described hereabove, refers to a non-resonant transmissionfrequency lying within the linear region 8 (FIG. 2), higher than theresonant peak 2. It will be appreciated however that in alternativeembodiments frequency-controlled power regulation may be achieved whenthe transmission frequency lies in the lower linear region of theresonance curve. Nevertheless, for certain embodiments, the selection oftransmission frequencies in the higher linear 8 may be preferred,particularly where peak detection, as described above, is required.

Referring back to FIG. 1, various transmitters 122 and receivers 124 maybe used for the communication channel 120. Where, as is often the casefor inductive systems, the primary and secondary coils 220, 320 aregalvanically isolated optocouplers, for example, may be used. A lightemitting diode serves as a transmitter and sends encoded optical signalsover short distances to a photo-transistor which serves as a receiver.However, optocouplers typically need to be aligned such that there is aline-of-sight between transmitter and receiver. In systems wherealignment between the transmitter and receiver may be difficult toachieve, optocoupling may be inappropriate and alternative systems maybe preferred such as ultrasonic signals transmitted by piezoelectricelements or radio signals such as Bluetooth, WiFi and the like.Alternatively the primary and secondary coils 220, 320 may themselvesserve as the transmitter 122 and receiver 124.

In certain embodiments, an optical transmitter, such as a light emittingdiode (LED) for example, is incorporated within the secondary unit 300and is configured and operable to transmit electromagnetic radiation ofa type and intensity capable of penetrating the casings of both thesecondary unit 300, and the power outlet 200. An optical receiver, suchas a photodiode, a phototransistor, a light dependent resistors of thelike, is incorporated within the power outlet 200 for receiving theelectromagnetic radiation.

Reference to the block diagram of FIG. 6, it is a particular feature ofcertain embodiments of the invention that an inductive communicationschannel 2120 is incorporated into the inductive power transfer system2100 for transferring signals between a inductive power outlet 2200 anda remote secondary unit 2300. The communication channel 2120 isconfigured to produce an output signal S_(out) in the power outlet 2200when an input signal S_(in) is provided by the secondary unit 2300without interrupting the inductive power transfer from the outlet 2200to the secondary unit 2300.

The inductive power outlet 2200 includes a primary inductive coil 2220wired to a power source 2240 via a driver 2230. The driver 2230 isconfigured to provide an oscillating driving voltage to the primaryinductive coil 2220, typically at a voltage transmission frequency f_(t)which is higher than the resonant frequency f_(R) of the system.

The secondary unit 2300 includes a secondary inductive coil 2320, wiredto an electric load 2340, which is inductively coupled to the primaryinductive coil 2220. The electric load 2340 draws power from the powersource 2240. Where the electric load 2340 requires a direct currentsupply, for example a charging device for an electrochemical cell or thelike, a rectifier 2330 may be provided to rectify the alternatingcurrent signal induced in the secondary coil 2320.

An inductive communication channel 2120 is provided for transferringsignals from the secondary inductive coil 2320 to the primary inductivecoil 2220 concurrently with uninterrupted inductive power transfer fromthe primary inductive coil 2220 to the secondary inductive coil 2320.The communication channel 2120 may provide feedback signals to thedriver 2230.

The inductive communication channel 2120 includes a transmission circuit2122 and a receiving circuit 2124. The transmission circuit 2122 iswired to the secondary coil 2320, optionally via a rectifier 2330, andthe receiving circuit 2124 is wired to the primary coil 2220.

The signal transmission circuit 2122 includes at least one electricalelement 2126, selected such that when it is connected to the secondarycoil 2320, the resonant frequency f_(R) of the system increases. Thetransmission circuit 2122 is configured to selectively connect theelectrical element 2126 to the secondary coil 2320. As noted above, anydecrease in either the inductance L or the capacitance C increases theresonant frequency of the system. Optionally, the electrical element2126 may be have a low resistance for example, with a resistance sayunder 50 ohms and Optionally about 1 ohm.

Typically, the signal receiving circuit 2124 includes a voltage peakdetector 2128 configured to detect large increases in the transmissionvoltage. In systems where the voltage transmission frequency f_(t) ishigher than the resonant frequency f_(R) of the system, such largeincreases in transmission voltage may be caused by an increase in theresonant frequency f_(R) thereby indicating that the electrical element2126 has been connected to the secondary coil 2320. Thus thetransmission circuit 2122 may be used to send a signal pulse to thereceiving circuit 2124 and a coded signal may be constructed from suchpulses.

According to some embodiments, the transmission circuit 2122 may alsoinclude a modulator (not shown) for modulating a bit-rate signal withthe input signal S_(in). The electrical element 2126 may then beconnected to the secondary inductive coil 2320 according to themodulated signal. The receiving circuit 2124 may include a demodulator(not shown) for demodulating the modulated signal. For example thevoltage peak detector 2128 may be connected to a correlator forcross-correlating the amplitude of the primary voltage with the bit-ratesignal thereby producing the output signal S_(out).

In other embodiments, a plurality of electrical elements 2126 may beprovided which may be selectively connected to induce a plurality ofvoltage peaks of varying sizes in the amplitude of the primary voltage.The size of the voltage peak detected by the peak detector 2128 may beused to transfer multiple signals.

FIG. 7 is a graph showing how the amplitude of the operational voltagevaries according to the transmission frequency. It is noted that thevoltage is at its highest when the transmission frequency is equal tothe resonant frequency f_(R) of the system, this maximum amplitude isknown as the resonance peak 2. If the resonant frequency f_(R) of thesystem increases, a new resonance peak 2′ is produced.

According to another embodiment of the invention, an inductive powertransfer system 2100 operates at a given transmission frequency f_(t)which is higher than the resonant frequency f_(R) of the system. Thenormal operating voltage V_(t) is monitored by the voltage peak detector2128. When the electric element 2126 is connected to the secondaryinductive coil 2320 the resonant frequency of the system increases.Therefore, the operating voltage increases to a higher value V_(t)′.This increase is detected by the voltage peak detector 2128.

It is noted that in contradistinction to prior art inductive signaltransfer systems such as described in U.S. Pat. No. 5,455,466 to TerryJ. Parks and David S. Register, the present invention enables datasignals to be transferred from the secondary coil 2320 to the primarycoil 2220 concurrently with inductive transfer of power from the primarycoil 2220 to the secondary coil 2320. Consequently, the signal transfersystem may be used to provide feedback signals for real time powerregulation.

FIG. 8 shows an exemplary circuit diagram of an inductive power outlet7200 and a secondary unit 7300, according to another embodiment of theinvention. An inductive feedback channel 7120 is provided fortransferring signals between the coils concurrently with uninterruptedinductive power transfer.

The inductive power outlet 7200 comprises a primary coil 7220 driven bya half-bridge converter 7230 connected to a power source 7240. Thehalf-bridge converter 7230 is configured to drive the primary coil 7220at a frequency higher than the resonant frequency of the system. Thesecondary unit 7300 comprises a secondary coil 7320 wired to the inputterminals T₁, T₂ of a rectifier 7330, and an electric load 7340 wired tothe output terminals T₃, T₄ of the rectifier 7330.

The inductive feedback channel 7120 comprises a transmission circuit7122, in the secondary unit 7300 and a receiving circuit 7124 in theinductive power outlet 7200. The transmission circuit 7122 comprises anelectrical resistor 7126 connected to the rectifier 7330 via a powerMOSFET switch 7125. A modulator 7123 may provide an input signal S_(in)to the power MOSFET 7125.

It is noted that in this embodiment the transmission circuit 7122 iswired to one input terminal T₁ and one output terminal T₃ of therectifier 7330. This configuration is particularly advantageous as, evenwhen the transmission circuit 7122 is connected, the resistor 7126 onlydraws power from the system during one half of the AC cycle, therebysignificantly reducing power loss.

The receiving circuit 7124 includes a voltage peak detector 7128 that isconfigured to detect increases in the transmission voltage, and ademodulator 7129 for producing an output signal S_(out).

With reference now to FIG. 9, a flowchart is presented showing the mainsteps in a method for transferring a signal from the secondary inductivecoil to a primary inductive coil of an inductive power transfer system.The method includes the following steps:

-   Step (i)—connecting the primary inductive coil to a voltage monitor    for monitoring the amplitude of a primary voltage across the primary    coil;-   Step (ii)—connecting the secondary inductive coil to a transmission    circuit for selectively increasing the resonant frequency of the    inductive power transfer system;-   Step (iii)—providing an oscillating voltage to the primary inductive    coil at an initial transmission frequency higher than the resonant    frequency thereby inducing a voltage in the secondary inductive    coil;-   Step (iv)—using the transmission circuit to modulate a bit-rate    signal with the input signal to create a modulated signal and    connecting the electrical element to the secondary inductive coil    intermittently according to the modulated signal, and-   Step (v)—using the voltage monitor to cross-correlate the amplitude    of the primary voltage with the bit-rate signal for producing an    output signal.

Therefore, the inductive communication channel 2120 may be used totransfer a feedback signal from the secondary inductive coil to theprimary inductive coil for regulating power transfer across an inductivepower coupling as described above.

It will be appreciated that embodiments of the present invention may beuseful in a wide range of applications. Inductive power receivers may beused to wirelessly provide power for a variety of electrical devices.Embodiments of the present invention may be integrated into suchinductive power receivers. In particular, because non-resonanttransmission uses lower transmission voltages, heat loss from thenon-resonant system is lower. Thus embodiments of the current inventionmay be of particular use when incorporated within high powerapplications such as power tools, kitchen appliances, bathroomappliances, computers, media players, office equipment and the like.

The reduced heat loss, associated with embodiments of the non-resonantsystems of the invention, is particularly useful when heat dissipationis difficult for example when power receiver has small dimensions or forheat-sensitive equipment such as measuring devices. Also, it isdesirable that devices implanted into a living body do not dissipatelarge amounts of heat into the body. Therefore, non-resonant inductivetransfer is well suited to implanted devices, such as pace makers,trackers and the like.

It is also noted that in recent years public concern about the threat ofa global energy crisis has resulted in a greater emphasis being placedupon optimizing the efficiency of energy transfer. It is difficult toachieve more demanding specifications using existing technology and, inthis context, embodiments of the present invention may be used toprovide high powers with very low energy losses. Consequently thecurrent invention is an important element in the drive for greaterefficiency.

Furthermore embodiments of the present invention may be advantageouslyutilized in inductive power transfer systems in any of the variousapplications in which power is transferred from a primary coil to aremote secondary coil. Amongst others, such applications include:

-   -   inductive chargers for use charging electronic devices,    -   inductive power adaptors for powering electronic devices such as        computers, televisions, kitchen appliances, office equipment and        the like,    -   medical applications in which power is transferred remotely to        devices implanted in a patient,    -   communications with remote RFID tags,    -   military application in which power is transferred across thick        armored plating,    -   communication or inductive energy transfer to secondary        inductive coils buried underground.    -   communication or inductive energy transfer to secondary        inductive coils submerged under water, for example in submarine        applications, and    -   communication or inductive energy with secondary coils which are        moving relative to the primary coil.

Thus, by using a transmission voltage oscillating at a frequencydifferent from the resonant frequency of the system, the inductivetransfer system has a higher tolerance to environmental fluctuations andvariations in inductive coil alignment than other transfer systems andthe frequency may be used to regulate power transfer. Moreover, when thetransmission frequency is higher than the resonant frequency of thesystem, a peak detector may be used to indicate hazards and provide aninductive communication channel.

Energy Efficient Inductive System

Reference is now made to the block diagram of FIG. 10A representingselected components of an embodiment of an energy efficient inductivepower transfer system 1000. The inductive power transfer system 1000includes an inductive power outlet 1200 and an inductive power receiver1300 and is configured to switch between transmission mode and standbymode.

In standby mode, the system 1000 may be dormant with the inductive poweroutlet 1200 and inductive power receiver 1300 waiting for an activationsignal before transitioning to transmission mode. In transmission mode,the inductive power system 1000 is configured and operable to draw powerfrom a power supply 1240, such as a mains electricity supply, a vehiclebattery, a power generator, fuel cell or the like, to an electric load1340.

It will be appreciated, that such an inductive power transfer system1000 may significantly reduce power losses associated with prior artpower transfer systems. During the standby mode little or no power maybe drawn from the power supply 1240. The inductive power outlet 1200 maybe configured to switch to transmission mode only in the presence of asuitable inductive power receiver 1300. Furthermore, the system 1000 maybe operable to revert to standby mode when no power need be transferred,for example when the inductive power receiver 1300 is removed or theelectric load 1340 requires no further power. Thus power is only drawnby the system 1000 when actually required. Various activation andtermination protocols may be used with the system, such as describedhereinbelow.

Referring now to the flowchart of FIG. 10B, the inductive power transfersystem 1000 may switch between standby mode and transmission mode by anumber of pathways. When in standby mode, the inductive power outlet1200 or the inductive power receiver 1300 may be configured to wait foran activation signal. If such an activation signal is received, thesystem 1000 may switch to transmission mode. Where appropriate,activation of the system 1000 may involve an initial trigger signalactivating the inductive power outlet 1200 and an authentication processconfirming the presence of a suitable inductive power receiver 1300.

When in transmission mode, the inductive power transfer system 1000 maybe configured to periodically transfer signals between the inductivepower receiver 1300 and the inductive power outlet 1200, such asdescribed hereinabove in relation to FIG. 5, for example.

As detailed below, various transmission signals may be used with thesystem, for example, instructions may be sent from the inductive powerreceiver 1300 to the inductive power outlet 1200 to increase power by acertain interval, to decrease power by a certain interval, to maintainthe same power, to terminate power transfer or the like. Where no suchtransmission signals are received, the inductive power outlet 1200 maybe configured to stop driving the primary inductor 1220 and to revert tothe standby mode.

In particular, the inductive power transfer system 1000 may beconfigured to revert to standby mode when a termination signal istransferred between the inductive power receiver 1300 and the inductivepower outlet 1200. Where appropriate, the inductive power receiver 1300may be configured to send a termination signal to the inductive poweroutlet 1200 when the electric load 1340 no longer requires power. Forexample, where the electric load 1340 is an electrochemical cell beingcharged by an inductive charger, say, a termination signal may begenerated when the electrical cell is fully charged.

It will be appreciated that an inductive power transfer system such asdisclosed herein may reduce significantly the amount of power drawn bydormant power adaptors, chargers and the like.

Referring back to FIG. 10A, the system 1000 may include a triggermechanism 1400 and a signal transfer mechanism 1120. The triggermechanism 1400 may be used while the inductive power transfer system1000 is in the standby mode, to provide an initial trigger to generatean activation signal such that the inductive power transfer system 1000switches to transmission mode. The signal transfer mechanism 1120 mayprovide a channel for the inductive power receiver 1300 to sendinstruction signals, such as identification signals, authenticationsignals, transmission signals, termination signals or the like to theinductive power outlet 1200.

The inductive power outlet 1200 of the inductive power transfer system1000 includes a primary inductor 1220 such as a primary inductive coil,for example, connectable to the power supply 1240 via a driver 1230. Thedriver 1230 provides the electronics necessary for supplying anoscillating voltage to the inductive coil 1220. The inductive powerreceiver 1300 typically includes a secondary inductor 1320, such as asecondary inductive coil, a regulator 1330 and an electrical load 1340.

The secondary inductive coil 1320 is configured to inductively couplewith the primary inductive coil 1220 of the inductive power outlet 1200.Where required, the regulator 1330 may include a rectifier to convertalternating current induced across the secondary coil 1320 to a directcurrent signal for supplying the electrical load 1340. A rectifier 1330may be necessary, for example, where the electrical load 1340 comprisesan electrochemical cell to be charged.

The trigger mechanism 1400 may control the connection between the powersupply 1240 and the inductive power outlet 1200. The trigger mechanism1400 may include a circuit breaker 1420 and a trigger sensor 1440.Optionally, trigger mechanism 1400 may further include an auxiliarypower source 1460 for providing power when the inductive power outlet1200 is disconnected from its power supply 1240. Various auxiliary powersources 1460 may be used in embodiments of the trigger mechanism 1400such as electrochemical cells, capacitors and the like, which may beconfigured to store energy while the inductive power outlet 1200 isconnected to the power supply 1240 for use when the inductive poweroutlet 1200 is disconnected. Still other auxiliary power sources mayinclude electricity generating elements such as solar cells,piezoelectric elements, dynamos or the like.

The circuit breaker 1420 may be configured to receive a disabling signalfrom the trigger and in response to provide an electrical connectionbetween the power supply 1240 and the inductive power outlet 1200.Various circuit breakers 1420 may be used to disconnect the inductivepower outlet 1200 from the power supply 1240 as suit requirements. Forexample, an electronic switch may be provided such as a Metal-OxideSemiconductor Field-Effect Transistor (MOSFET) or the like the gateterminal of which may be configured to receive the electrical signalssent by the trigger sensor 1440. Other circuit breakers may include forexample, a single pole switch, a double pole switch, a throw switch orthe like.

The trigger sensor 1440 is configured to detect a release signalindicating the proximity of a possible inductive power receiver 1300.The trigger 1440 may be further configured to disable the circuitbreaker 1420 when the release signal is detected. Optionally, anactivator 1480 incorporated into the inductive power receiver 1300 isconfigured to produce the release signal which is detectable by thetrigger 1440.

In one embodiment the trigger mechanism 1400 may include a magneticdetector such as a Hall Effect switch, reed switch or the like. Themagnetic switch may be configured to detect an increase in magneticfield as a result of the approach of an activating magnetic elementassociated with the inductive power receiver 1300. It will beappreciated that a Hall Effect switch may be configured to detect theapproach of an alignment magnet associated with the inductive powerreceiver 1300 which further functions as the activating magnetic element1480 for the trigger mechanism 1400. It will be further appreciated thatother magnetic switches may be used in other embodiments of the triggermechanism as will occur to the skilled practitioner. Still otherembodiments of the trigger mechanism may be used, for example, asdescribed in the applicants co-pending patent applicationPCT/IL2010/001013 which is incorporated herein by reference.

The signal transfer system 1120 may include an inductive feedbackchannel 7120 such as described hereinabove in relation to FIG. 8. Theregulator 1330 of the inductive power receiver may be in communicationwith a transmission circuit 1122 including a signal generator 1123, aswitching unit 1125 and an ancillary load 1340. The signal generator1123 may be a modulator 7123 such as described in FIG. 8. The switchingunit 1125 may be a MOSFET 7125 such as described in FIG. 8. Variously,the ancillary load 1126 may be an electrical resistor 7126 such asdescribed in FIG. 8, although other electrical elements such ascapacitors, inductors and the like may alternatively or additionallyserve as the ancillary load 1126. The transmission circuit 1122 may thusmodulate the power drawn by the secondary inductor 1320. The modulatedpower may be detected by a signal detector 1124 associated with theinductive power outlet 1200.

The inductive power outlet 1200 includes a signal detector 1124comprising a peak detector 1128 and a processor 1129. The peak detector1128 may be configured to detect peaks in primary voltage across theprimary inductor or primary current supplied to the primary inductor.Thus, the peak detector 1128 may be able to detect when the ancillaryload is connected to the secondary inductor 1320. The processor 1129,such as the demodulator 7129 described above in relation to FIG. 8, maybe provided to determine the frequency of peak pulses.

The signal transfer system 1120 may be used to transmit instructionsignals such as identification signals, authentication signals,transmission signals, termination signals or the like to the inductivepower outlet 1200 in the form of peak pulses having characteristicfrequencies.

The regulator 1330 of the inductive power receiver 1300, which mayinclude a controller, rectifier, capacitors, microcontroller, voltagemonitor or the like, is in communication with the transmission circuit1122.

The regulator 1330 may be operable to monitor induced secondary voltageacross the secondary inductor 1320 and to compare the induced voltagewith reference values. By comparing the secondary voltage with thresholdvalues, the regulator 1330 may determine whether the secondary voltagelies within a permissible range of values. Accordingly, instructionsignals may be selected by the regulator 1330 and generated by thetransmission circuit 1122 instructing the inductive power outlet 1200 toadjust the induced voltage across the secondary inductor 1320.

It will be appreciated that in standby mode no voltage is induced acrossthe secondary inductor 1320. As outlined in greater detail below, instandby mode, the regulator 1320 and transmission circuit 1122 may befurther operable to respond to an activation voltage pulse inducedacross secondary inductor 1320 by generating an identificationinstruction signal (ID signal). The ID signal may be detected by theinductive power outlet 1200 thereby confirming the presence of theinductive power receiver 1300 and optionally its required operatingparameters.

Reference is now made to FIG. 11A showing selected stages of a possibleprotocol for transition from standby phase to the transmission phase inthe inductive power outlet. In standby phase, the dormant inductivepower outlet waits for a release signal 1002.

The release signal indicates to the inductive power outlet that acompatible inductive power receiver may have been placed withintransmission range. Such a release signal may be inter alia a change inlocal magnetic field associated with a trigger magnet in the inductivepower receiver. Accordingly in one embodiment the inductive power outletincorporates a Hall switch which is configured to detect changes in thelocal magnetic field. Other release signal mechanisms will occur tothose skilled in the art such as signals detectable using piezoelectricelements, light sensors, audio sensors and the like as suitrequirements.

If no release signal is received the outlet remains in standby mode1004. When a release signal is detected by the outlet an authenticationprocess 1005 is initiated during which the presence of the inductivepower receiver is confirmed. The authentication process may start by thedriver of the primary inductor producing an initial power of sufficientintensity to induce an activation voltage pulse across the secondaryinductor of the inductive power receiver 1006. For example, a primaryvoltage may be driven across the primary inductor such that anactivation voltage pulse of eight volts is induced across the secondaryinductor.

The inductive power outlet may be operable to detect an ID signal inresponse to the initial power burst 1008. If the inductive power outletreceives an ID signal response from a recognized inductive powerreceiver, then the ID signal may be identified 1010 and the modeswitched to transmission mode 1016. Optionally, depending upon theidentity of the ID signal, an initial transmission power level may beselected 1012 according to what ID signal is received and the primaryinductor driven with the initial transmission power level 1014.Alternatively, the initial transmission power level may be thetransmission power level of the initial power burst.

Optionally, the initial power burst across the primary inductor may berepeated for a fixed number of iterations before the inductive poweroutlet reverts to standby mode. Variously, the driving voltage of theinitial power burst may be constant or changing. According to oneembodiment, the driver of the inductive power outlet may be operable toproduce an initial 15 millisecond burst of oscillating voltage acrosswhich may repeated, say every 256 milliseconds or so. After fiveiterations or so, if no ID signal is received, the inductive poweroutlet may revert to standby mode.

Various ID signals may be used in embodiments of the present disclosure,for example, where the inductive power outlet includes a peak detector,as described hereinabove, a transmission circuit may be used to modulatethe primary voltage across the primary inductor, or primary currentdrawn by the primary inductor, with peak pulses having characteristicfrequencies which are identifiable as generated by recognized inductivepower receivers. In one embodiment, ID signals may peak pulses havingcharacteristic frequencies selected from 500 hertz, 1 kilohertz and 8kilohertz. The selected characteristic frequency of the ID signal mayprovide further instructions to the inductive power outlet for examplerelating to required transmission parameters, user specific data,billing information or the like.

The power level of the induced voltage may be regulated by adjusting avariety of parameters of the driving voltage. For example, wherenon-resonant power transmission is used, such as described hereinabove,the power level may be determined by the selected operating frequency.Optionally, the initial voltage across the primary inductor may besteadily increased by decreasing the driving frequency from 476kilohertz to 313 kilohertz during the initial burst. Alternatively, athe power level may be selected by adjusting the duty cycle or amplitudeof the driving voltage.

Reference is now made to FIG. 11B representing a possible transmissionmode protocol for use with an inductive power outlet. Optionally, such aprotocol may be initiated by the transition protocol of FIG. 11A,alternatively an inductive power outlet may be activated in other ways,such as by manually operating a power switch, connecting to a mainspower supply or the like.

In transmission mode, the inductive power outlet may be operable todrive the primary inductor for a limited time duration 1020, for examplefor 10 milliseconds or so. At the end of the limited time duration, theoutlet may be operable to terminate the operation 1036 unless aninstruction signal is received 1022. Such a system may enable an energyefficient inductive power outlet to draw power only when required and toshut down when not needed. If an instruction signal is received from theinductive power receiver, the signal may be identified 1024 and actedupon, for example, as follows:

-   -   if a perpetuation signal P-SAME is received from the inductive        power receiver 1026, then the driver may continue to drive the        primary inductor for a further duration;    -   if a first power increase signal P-UP is received from the        inductive power receiver 1028, then the driver may increase the        power level by a first incremental value 1029;    -   if a second power increase signal P-DUP is received from the        inductive power receiver 1030, then the driver may increase the        power level by a second incremental value 1031;    -   if a power decrease signal P-DOWN is received from the inductive        power receiver 1032, then the driver may decrease the power        level by an incremental value 1033; or    -   if a termination signal END-SIG is received from the inductive        power receiver 1034, then the driver may be terminated 1036,        thereby ceasing to drive the primary inductor and the inductive        power outlet reverting to standby mode.

To better explain the transmission protocol and for illustrativepurposes only, an example of the protocol is described below in whichthe inductive power outlet drives a non-resonant transmission voltage.The protocol may also be applicable to resonant transmission systems.

The instruction signals may comprise modulated peak pulses with eachsignal having a characteristic frequency. In one particular embodimentthe perpetuation signal P-SAME may have a characteristic frequency of500 hertz, the first power increase signal P-UP may have acharacteristic frequency of 8 kilohertz, the second power increasesignal P-DUP may have a characteristic frequency of between 1.5 and 5kilohertz, the termination signal END-SIG may have a characteristicfrequency of 250 hertz. It will be appreciated that other characteristicfrequencies may alternatively be used. Indeed, where required, otherinstruction signals, such as additional power decrease signal, forexample, may be additionally or alternatively transferred as suitrequirements.

Referring again to FIG. 2, as noted above, where the transmissionfrequency is selected from the non-resonant region 8 above the resonantfrequency of the system the output power of the secondary inductor maybe regulated by increasing or decreasing the driving frequency byincremental amounts. According to one embodiment in which thetransmission frequency is around 10 megahertz the incremental frequencysteps δf may be selected from within a permissible range of 277kilohertz to 357 kilohertz or so.

In one system the driver 1230 (FIG. 10) of the inductive power outletmay include a microcontroller unit operable to calculate the incrementalfrequency value f_(op+1)−f_(op) according to the formula:

${f_{{op} + 1} - f_{op}} = {\frac{F_{sys}}{{divider}\mspace{14mu} {value}} - \frac{F_{sys}}{{{divider}\mspace{14mu} {value}} - 1}}$

where F_(sys) is the transmission frequency of the driver, and thedivider value is an integer value. Where required, different incrementalvalues may be used for increasing and decreasing the voltage or power.

As noted, two power increase signals P-UP and P-DUP may requestdifferent incremental power increases. Accordingly the second powerincrease signal P-DUP may be used to step up power by larger increments,say twice the size of the standard increments. This may be useful forexample where the initial voltage is particularly low.

Turning now to the inductive power receiver, reference is made to FIG.11C showing possible operational steps during inductive power reception.The inductive power receiver may be activated when a voltage is inducedacross the secondary inductor 1040, when the regulator may detect theactivation voltage 1042 an identification signal may be sent to theinductive power outlet 1044.

Such an identification signal (ID signal) may serve to switch theinductive power transmitter to transmission mode as described above inrelation to FIG. 11A. For example, an induced voltage of about 8V andproducing a current of about 3 milliamps and lasting about 5milliseconds or so, may power a microcontroller associated with theregulator to activate the sending of an ID signal to the inductive poweroutlet. In one embodiment, a transmission circuit 1122 (FIG. 10) may beused to produce a modulated peak pulse having a characteristic frequencyselected from 500 hertz, 1 kilohertz, 8 kilohertz or the like.Variously, the inductive power receiver may select an ID signal suchthat predetermined transmission parameters may be selected for operatingthe inductive power outlet.

It is noted that during power transfer, the inductive power receiver isoperable to periodically send instruction signals to the inductive poweroutlet. The instruction signals may be selected according to variousfactors as outlined below.

Where, the inductive power receiver is operable to detect anend-of-charge command EOC-SIG indicating that the electric load, such asan electrochemical cell or the like, requires no more power 1046. Ifsuch an end-of-charge command is detected, the inductive power receivermay be operable to send a termination signal END-SIG to the inductivepower transmitter 1064. As outlined above in relation to FIG. 11B, thetermination signal instruct the inductive power outlet to revert tostandby mode. According to one embodiment, the termination signal maycomprise a modulated peak pulse having a characteristic frequency of 250hertz. It will be appreciated that such a termination mechanism mayenable an energy efficient inductive power transfer system to draw poweronly when required and to shut down when not needed thereby reducingenergy wastage.

If no end-of-charge command is detected, the regulator may be configuredto compare the output of the secondary inductor to at least onereference value 1048. For example, the regulator may compare secondaryvoltage to reference values stored in a memory element. Alternatively,reference values may be calculated by a processor associated with theinductive power receiver to suit requirements.

If the power is below a first lower threshold value Th₁ 1050, a firstpower increase signal P-UP may be sent to the inductive power outlet1058. The regulator may further compare the power to a second thresholdvalue Th₂ 1052, if the power is also lower than the second thresholdvalue Th₂ a second power increase signal P-DUP may be sent to theinductive power outlet 1056.

Where the power is above the first lower threshold value, the power maybe compared to at least one an upper threshold value Th₃ 1054. If thepower level is greater than the upper threshold value Th₃, then a powerdecrease signal P-DOWN may be sent to the inductive power outlet 1060.

It is particularly noted that where the power level is neither greaterthan the upper threshold value Th₃ nor lower than the lower thresholdvalue Th₁, then a perpetuation signal P-SAME may be sent to theinductive power outlet 1062. Thus when even when no action is required asignal is sent at least one instruction signal may be sent to theinductive power outlet during each time duration. Accordingly, theinductive power receiver may periodically indicate its continuedpresence to the inductive power outlet. It will be appreciated that whenthe inductive power receiver is removed from the inductive power outlet,no instruction signals will be passed therebetween. As indicated abovein relation to FIG. 11B, the inductive power outlet may be configured toshut down when no such signal is received.

Although only five instruction signals are described hereinabove, otherinstruction signals may be additionally be transferred as required.Various instructions may occur to those skilled in the art, for exampleindicating that the power is outside still further threshold values,requesting greater power resolution or such like.

The scope of the present invention is defined by the appended claims andincludes both combinations and sub combinations of the various featuresdescribed hereinabove as well as variations and modifications thereof,which would occur to persons skilled in the art upon reading theforegoing description.

In the claims, the word “comprise”, and variations thereof such as“comprises”, “comprising” and the like indicate that the componentslisted are included, but not generally to the exclusion of othercomponents.

What is claimed is:
 1. A signal transmission circuit for an inductivepower receiver, the signal transmission circuit operable to regulateinductive power transmission across an inductive power coupling, theinductive power coupling comprising at least one primary inductive coilassociated with an inductive power outlet and a secondary inductive coilassociated with the inductive power receiver, the inductive powerreceiver comprising: the secondary inductive coil connectable to anelectric load; the signal transmission circuit; and at least oneelectrical element selectively connectable to the secondary inductivecoil by a switching unit; wherein: the signal transmission circuit isconfigured to generate at least one coded signal by connecting theelectrical element to the secondary inductive coil in pulses having anidentifiable characteristic frequency such that the coded signal isdetectable by a signal reception circuit associated with the inductivepower outlet.
 2. The signal transmission circuit of claim 1, wherein thecharacteristic frequency is selected from a group consisting of: 250hertz, 500 hertz, 1 kilohertz, 1.5 kilohertz, 5 kilohertz and 8kilohertz.
 3. The signal transmission circuit of claim 1, wherein thecoded signal comprises an identification signal, the identificationsignal transmitted in response to an initial power pulse received fromthe inductive power outlet.
 4. The signal transmission circuit of claim3, wherein the identification signal is selected from at least: a firstsignal to instruct the inductive power outlet to drive the at least oneprimary inductive coil at a first operating power; and a second signalto instruct the inductive power outlet to drive the at least one primaryinductive coil at a second operating power.
 5. The signal transmissioncircuit of claim 1, wherein the coded signal comprises a terminationsignal to instruct the inductive power outlet to cease driving theprimary inductive coil when the coded signal is detected.
 6. The signaltransmission circuit of claim 1, wherein the coded signal comprises aperpetuation signal, the perpetuation signal transmitted to theinductive power outlet when power received lies within a permissiblerange of values to instruct the inductive power outlet to continuedriving the primary inductive coil at the same power level.
 7. Thesignal transmission circuit of claim 1, wherein the coded signalcomprises a power increase signal, the power increase signal transmittedto the inductive power outlet when the power received lies below athreshold value.
 8. The signal transmission circuit of claim 1, whereinthe coded signal comprises a power decrease signal, the power decreasesignal transmitted to the inductive power outlet when the power receivedlies above a threshold value.
 9. A signal reception circuit for aninductive power outlet operable to regulate inductive power transmissionacross an inductive power coupling, the inductive power couplingcomprising at least one primary inductive coil associated with theinductive power outlet and a secondary inductive coil associated with aninductive power receiver, the inductive power outlet comprising: the atleast one primary inductive coil connectable to a power supply; at leastone driver configured to provide an oscillating voltage across the atleast one primary inductive coil; and the signal reception circuitwherein: the signal reception circuit comprises a monitor wired to theat least one primary inductive coil, the monitor configured to detect atleast one coded signal generated by a signal transmission circuit of theinductive power receiver connecting an electrical element to thesecondary inductive coil; the at least one coded signal detectable as apulse in primary voltage or primary current, the pulse having anidentifiable characteristic frequency.
 10. The signal reception circuitof claim 9, wherein the characteristic frequencies selected from atleast one of a group consisting of: 250 hertz, 500 hertz, 1 kilohertz,from 1.5 kilohertz to 5 kilohertz and 8 kilohertz.
 11. The signalreception circuit of claim 9, wherein the coded signal comprises anidentification signal selected from at least: a first signal instructingthe inductive power outlet to drive the at least one primary inductivecoil at a first operating power; and a second signal instructing theinductive power outlet to drive the at least one primary inductive coilat a second operating power.
 12. The signal reception circuit of claim9, wherein the coded signal comprises a termination signal instructingthe inductive power outlet to cease driving the primary inductive coilwhen the coded signal is detected.
 13. The signal reception circuit ofclaim 9, wherein the coded signal comprises a perpetuation signal, theperpetuation signal instructing the inductive power outlet to continuedriving the primary inductive coil at the same power level.
 14. Thesignal reception circuit of claim 9, wherein the coded signal comprisesa power increase signal instructing the inductive power outlet toincrease operating power.
 15. The signal reception circuit of claim 9,wherein the coded signal comprises a power decrease signal instructingthe inductive power outlet to decrease operating power.
 16. A method forregulating inductive power transmission from an inductive power outletto an inductive power receiver across an inductive coupling, theinductive power coupling comprising at least one primary inductive coilassociated with an inductive power outlet and a secondary inductive coilassociated with the inductive power receiver, the method comprising:driving the primary inductive coil at an initial operating power;monitoring induced voltage in the secondary inductive coil; a signaltransmission circuit associated with the inductive power receiverconnecting an electrical element to the secondary inductive coil inpulses having an identifiable characteristic frequency therebytransmitting at least one control signal; and a signal reception circuitassociated with the inductive power outlet detecting the control signalas pulses in primary voltage or primary current with the identifiablecharacteristic frequency.
 17. The method of claim 16 wherein thecharacteristic frequency is selected from at least one of a groupconsisting of: 250 hertz, 500 hertz, 1 kilohertz, 1.5 kilohertz, 5kilohertz and 8 kilohertz.
 18. The method of claim 16 furthercomprising: the signal reception circuit detecting pulses in primaryvoltage or primary current having a characteristic frequency associatedwith an identification signal; and driving the primary inductive coil ata first operating power.
 19. The method of claim 16 further comprisingat least one of: if the signal reception circuit detects pulses inprimary voltage or primary current having a characteristic frequencyassociated with a power increase signal then increasing operating powerby an increment; and if the signal reception circuit detects pulses inprimary voltage or primary current having a characteristic frequencyassociated with a power decrease signal then decreasing operating powerby an increment.
 20. The method of claim 16 further comprising: thesignal reception circuit detecting pulses in primary voltage or primarycurrent having a characteristic frequency associated with a perpetuationsignal; and driving the primary inductive coil at same power.
 21. Themethod of claim 16 further comprising: the signal reception circuitdetecting pulses in primary voltage or primary current a characteristicfrequency associated with a termination signal, and ceasing to drive theprimary inductive coil.